This application note is applicable to any Flexible Printed Circuit (FPC) antenna from Siretta’s range of antennas.

At the time of publication, the following FPC antennas are available:

Objective

FPC antennas bring designers the benefits of being able to be bent to fit into available space within an enclosure, as well as having an extremely low profile and little weight. However, to be able to realise the data sheet specification of these antennas, it is important to instal them correctly.

The objective of this application note is to explain how to correctly instal an FPC antenna in an application without damaging it, while obtaining the best radio performance.

Solution

Background

An FPC antenna is made from a copper foil (forming the active radio part of the antenna) glued to a sheet of polyimide film. This results in a bendable antenna that is less than 0.15 mm thick. The polyimide film gives the antenna strength, preventing the copper foil from being damaged, while still retaining flexibility. Polyimide film is also a good electrical insulator, chemically stable, and does not attenuate radio signals.

The FPC antenna ships with adhesive transfer tape pre-applied to the antenna. The tape uses 3M low surface energy acrylic adhesive 300LSE which may be used to attach the antenna to many hard to bond materials such as polypropylene, polycarbonate and ABS plastic.

The antennas may be available with U.FL or MHF4 connectors. This is an ordering option. MHF4 is the latest RF connector and is slightly smaller than the U.FL connector. Generally, MHF4 is used for 5G applications and U.FL with older radio standards such as WiFi, GSM, UMTS and LTE.

Antenna Placement

FPC antennas do not require an external ground plane to work, and so are ground plane independent.

However, being ground plane independent does not mean that it is wise to place an FPC antenna close to a ground plane or other large metal surface. The ground plane will block the radio signal to/from the antenna. Most printed Circuit Boards (PCBs) contain ground planes, so in general it is wise to consider this. Place the antenna so that the PCB and any other metal objects in the path that the radio signals need to take to establish a radio link is minimised.

PCBs can also contain processors and high-speed clock lines. Again, it is advisable to keep the antenna separated from these potential sources of interference.

So, what is the recommended separation between FPC antenna and ground planes/large metal surfaces? There is no right answer to this question as it depends on many factors. However, Siretta suggests that 20 – 25 mm should be the minimum distance when the FPC antenna is co-planer to the PCB.

Another consideration for antenna placement is the polarisation of the antenna. Most modern radio data systems such as cellular, WiFi and IEEE802.15.4 expect to use vertical polarisation. Polarisation of the antennas at each end of the radio link ideally should be matched, and so the expectation is that the FPC antenna should be mounted in the vertically polarised position. However, in practice there are likely to be many reflection paths between both ends of the radio link. This will provide cross-polarization and make the antenna orientation somewhat irrelevant unless there is a clear line of sight between both ends of the radio link that has few reflection paths (such as a radio link across a field). Please read the Siretta Antennas 101 eBook to understand more about polarisation. To be vertically polarized, the antenna Z plane should point up to the sky.

Mounting surface

The main consideration for the mounting surface is that it is transparent to radio waves and will not reflect or absorb them. This generally means avoiding metals and other materials that are electrically conductive or magnetically permeable (since radio waves are electro-magnetic waves). Plastics, of any type, are generally good choices unless they are glass filled or coated with metallic paint.

The mounting surface can be flat but doesn’t have to be. One of the benefits of a FPC antenna is that it can be bent and mounted on curved surfaces. It is recommended that the bend radius be not less than 100 mm as otherwise excessive strain will be placed on the epoxy adhesive used in the construction of the antenna. Sirettas FPC antennas are characterised and tested on both flat and curved surfaces to ensure that the antenna meets expectations no mater how it is mounted.

Cable Management

The integrated 1.13 mm coaxial cable is part of the antenna and needs to be routed to the mating connector in a way that minimises noise interference. Do this by trying to keep it over grounded areas and avoiding high rf emission parts of the product such as processors, high speed clock lines and display drivers. Any bends in the cable should have a bend radius (90 degree bend) of no less than 9.1 mm otherwise the VSWR/Return Loss specification could be compromised.

At the mating connector, the cable should run flat along the PCB so that there is no leverage stress applied to the connector which could damage the connector and break the connection. If necessary, it is suggested that some hot melt glue be applied to the cable to attach it to the PCB to provide stress relief.

I-PEX MHF I and MHF 4 connectors

The I-PEX MHF I connector is also known as (and will mate with) Hirose U.FL, Amphenol AMC and Sunridge MCB connectors. The I-PEX MHF 4 connector is also known as (and will mate with) Murata HSC connectors.

These connectors may be attached either by hand, or by using an attachment tool designed for the purpose.
I-PEX attachment tool part numbers are:

I-PEX 90435-001 (MHF4)
I-PEX 90224-0001 MHF I

Please refer to documentation from I-PEX for the correct way to use these tools. If attaching by hand, please follow these instructions:

Instructions for mounting I-PEX MHF I and MHF 4 connectors (by hand)

Using the adhesive tape to bond the antenna to a surface

The ideal temperature at which to bond the FPC antenna to a surface is 20°C to 38°C. At this temperature the adhesive will have a very high initial adhesion. The bond strength will increase with time and temperature artier the antenna has been applied to a surface.

For the best bond strength, the surface to which the antenna is being attached should be dry, clean and well unified. If cleaning is required, use a cleaning solvent such as isopropyl alcohol.

Application below 10°C is not recommended since the adhesive becomes too firm to adhere readily. However, once properly applied, the adhesive will work satisfactorily at low temperatures.

Environmental

Each FPC antenna data sheet includes the operational temperature range for the antenna. These need to be respected as otherwise the bond to the surface on which the antenna is mounted could fail, especially if it is mounted on a curved surface.

Contact with solvents which could degrade the bonds of the adhesives used both in the antenna manufacture and to attach the antennas should be avoided.

Demonstration of Solution

Disclaimers and Waivers

Safety Disclaimer: The installation of this antenna should be carried out in accordance with local safety regulations. The manufacturer is not responsible for damages or injuries resulting from improper installation or use.

Professional Recommendation: For optimal performance and safety, we recommend installation by a qualified professional. Improper installation may void the warranty and could lead to poor performance or safety hazards.

Compliance Statement: Ensure compliance with all local building codes and electrical safety standards. The manufacturer is not liable for any violations of such regulations.

General/Ongoing Maintenance: Regular maintenance checks are essential for sustained performance and safety. Failure to conduct these checks could result in unexpected performance issues and safety risks.

Installation Confirmation: Upon installation, it is the responsibility of the installer to ensure that the antenna is securely mounted and functioning as intended. The manufacturer is not liable for issues arising from installation errors or oversights.

Additional Reading

The post How to Install and Use The Siretta ECHO FPC Antenna Range appeared first on Siretta Limited.

Frequency of Interest and Standard Plot Cuts – Interpretation and Further Analysis.

Below, we show how to read the 2D Radiation charts, on our datasheets, to determine the performance provided for a frequency band.

Overview

There are two types of radiation plot provided from the same data. The 2D representation is a standard spherical data format used by test laboratories. This data is per IEEE Std 149 (1979) ‘IEEE Standard Test Procedures for Antennas’ and uses the Phi axis rolling as per the ‘Great Circle Cut System’. Each of the standard datasheet cut planes may miss key information, as the maximum radiation point may not be present in the cut. The 3D plot shows an overview of the radiation energy at the spot frequency which is easier to visualise.

1440 MHz

1440 MHz XY                                                        XZ                                                                              YZ

1440 MHz

1440 MHz XY                                                        XZ                                                                              YZ

We can see from the two vertical cuts that the maximum radiation is better than displayed in the XY Horizontal plot. The 2 vertical cuts, in themselves, may also miss points that have better radiation at different angles. The 2D standard antenna plots only give a general indication of total performance and many plots are required to gain some insight into the overall performance. They are, however, more useful in determining values at specific points than the 3D plots.

The combination of the two different types of radiation plot allow for a more complete understanding of how the antenna performs. For each frequency band of interest, that your device will operate on, review the plots to ascertain if the particular antenna will work for you.

Key Take-aways:

1. That 2D XY Horizontal plot does not necessarily show the highest radiated energy.
The standard laboratory cuts do not always show the highest radiated energy, they are indicative of the overall pattern. However, they
are better for obtaining more accurate radiation levels than the 3D plot.
2. The 3D Plots are good for overall visualisation but more difficult to get exact radiation figures.
Use a combination of the two plot types, 2D and 3D, to obtain a better performance overview
3. There are other key parameters to consider like, VSWR / Return Loss and Radiation Efficiency.

About Siretta – Global manufacturer of IoT Solutions

A leading manufacturer and developer of IoT products, IoT software and IoT solutions. Our specialty being in providing these for Industrial markets and business to business applications. We have extensive knowledge and experience within IoT with a focus on cellular technologies in support of 2G (GPRS), 3G (UMTS), 4G (LTE), NB-IoT and LTE Category M.

Supplying products globally for over a decade in support of many blue-chip organisations with an unrivalled level of regional and local technical expertise and applications knowledge ensures we exceed customer expectations in support of varied applications and deployments.

Our portfolio includes cellular modems & terminals, routers, cellular network analysers, RF antennas including solutions for WLAN, LoRa and Sigfox. We offer RF cable assemblies and RF accessories. Frequencies are typically within the 75MHz – 5.8GHz range covering the HF, VHF, ISM, Cellular, GNSS frequencies. We also offer bespoke customer solutions and our design services
are supported by an experienced team of dedicated development & application engineers as well as software specialists offering complete end to end solutions with a heavy emphasis on high level
system design.

We are your partner of choice in enabling your IoT solutions.

The post 2D Radiation Plots appeared first on Siretta Limited.

The coax cable type and length of cable used will be one of the most significant factors that reduces the available signal, both received and transmitted. In general, cable lengths should be kept to a minimum and where lengths above 5m are required, a low loss type should be used.

The operating frequency of the system will also come into play and the lower the frequency the less loss there will be. Lower frequency signals also travel better in the air and through buildings giving better overall transmission performance.

Cable Attenuation

Attenuation is the term given to the loss of signal along a length of cable. When a signal is attenuated it is lessened, much like water pressure in a pipe, it starts out strong but over distance the pressure weakens. With an RF (Radio Frequency) signal the amount of attenuation is also linked to the frequency of the waveform as much as the resistance and other factors in the cable, which we explore later.

Fig 1.0 illustrates the spread of performance for some of the common cables (attenuation shown in dB per 100m).

What’s a dB? This is short for decibel and is a way to logarithmically express a ratio.
It is common to use this expression to describe the loss or gain of power.

This information is interesting but what does that really mean when we typically only have short cable feeds to the antennas of sub 20m. The next graph explores the difference between a standard RG58 cable and a low loss type like the SLL200 used in our cable assemblies.

Fig 1.1 The same cable performance but now for 5m 10m and 20m cable lengths. It can be seen how a short length of cable can reduce the signal from the antenna or device, especially at higher frequencies.

The cable has a resistance to the signal which reduces the voltage (a combination of: the signal travelling the length of the cable, coupling loss though magnetic fields with the shield, return loss from imperfections in the cable, tight bends and adapters joining lengths of cable). A hefty list of issues, all with small effects but all which add up to create a loss, worthy of consideration. Some of which cannot be mitigated against and others which are affected by installation practices or purchase choices.

Installing a larger diameter cable could be the first ‘go to’ answer but cost will also be a factor. A higher quality cable of the same type will generally be a better compromise. Quality manufacturing will prevent cable imperfections of the core where surface damage can result in signals returning back down the cable (return loss).

Copper Cable Draw down Process

At the frequencies we are concerned with: starting from the lower megahertz ISM bands and cellular bands from 700MHz upwards, all signals travel on the surface of the centre conductor. With that in mind, any damage to the centre core can cause transmission issues. For single events this is unlikely to be troublesome but indentation can be caused by the machinery making the cable. A damaged pulley wheel used in the initial copper draw down from a larger diameter to the correct size, could cause an indent at regular pitches which reflect part of the signal. Possible core damage through a draw down manufacturing process

Core imperfections

Imperfections on the surface of the central conductor can cause small parts of the signal to be reflected. A damaged pulley wheel in the wire draw down process could indent the wire at regular intervals causing a higher return loss than anticipated from the specification.

Coupling to the shield – foil or braid

Coupling is a mechanism by which an electric current in a cable produces an electromagnetic field that cuts across another conductor. In this case, the conductor is the cable shield which returns the current flow in the opposite direction. The energy lost in the coupling is part of the signal attenuation. Shown in the illustration is a cable with a 50-60% braid coverage. Whilst being a cheaper cable it is also less effective at shielding the core to outside interference. The size of the hole in the braid will let some frequencies pass through to the core. In addition, transient power spikes from mains cables laid parallel and next to the coax cable can cause signal distortion.

Whilst comms between devices may stay running, errors and retries for transmissions will use cellular bandwidth and could cost more depending on SIM contracts. With IoT devices passing small amounts of data back to server applications the extended transmissions will also affect modem battery life.

A device with a battery life expectancy of 5 years could be significantly reduced by staying powered up for longer to get transmissions completed each time it is scheduled to send data.

Impedance Mismatch – connectors / adaptors / cables

There are many RF connectors on the market and each will have its benefit, whether it be easy to connect/ disconnect or performance related. Joining 2 cable sections together will never be perfect and losses will occur. A lot of the time it might seem like there is only one cable linking to an antenna but, in reality there could be a small attachment cable inside the device. These cables typically have a PCB micro connector linking to a case mounted SMA connector with a very thin 1.13mm cable.

The more connections there are between the antenna and receiver electronic circuit, the more the signal is disturbed, distorted and reduced in strength.

An SMA connector is illustrated below and the path from cable to cable is clearly not a smooth continuous path of the same size. Given that the frequencies we are concerned with travel in the ‘skin’ or on the surface we can see the transitions on the surface of the pin and socket will disrupt the signal in some form. A small part of high frequency signals will get reflected back down the cable or trapped in larger parts of the connector pins.

Another feature of good connector design is ‘contact wipe’. Microscopic particles of dust and dirt can accumulate on the surface of unmated connections and can reduce the effective contact area for galvanic signal transmission. The female pin of the SMA connector has a scrape action that wipes the surface clean as the male pin is inserted. The same action also removes an oxidised surface to make a cleaner contact. Part of the signal passing through the connector will be through capacitive coupling and part through galvanic action (contact between the metal surfaces).

One or two cycles of connecting and disconnecting should clean the surface to provide the best signal through the connector.

Inside the body of the SMA Male nut is a small washer, shown in red, which will protect against moisture and dust ingress. The nut should be torque tightened (8-10in-lbs) to ensure a good seal and to prevent vibrations from loosening the nut.

Key Take-aways:

1. Avoid long cable runs where possible but use low loss types in lengths above 5m

The use of a quality, low loss cable means that you can keep as much of the signal collected by the antenna as possible. It also reduces the size of antenna required in an installation avoiding unsightly installations and targets for mindless vandalism.

2. Avoid intermediate connections and adaptors where possible

The use of multiple pieces of cable joined together with adaptors affects the signal quality and overall reliability of the system. Use them only as a temporary solution to trial installations or to adapt one connector type to another BUT, replace them with a single cable with the correct connectors on as soon as you can.

3. Be careful during cable installation and provide smooth bend transitions

If a quality cable is used, the affect of poor installation is lessened. As a rule of thumb, keep coaxial cables away from mains power cables by 100mm for 240V and 300mm for 415V. Avoid over manipulating the cable during installation and keep bends long and smooth. Manipulating low quality cable can breakdown the foil shield and open up the braid weave. Forcing the cable into tight bends and kinks can cause return loss.

4. When installing outdoors pay attention to connection points

Check the nut torque specifications to ensure the seal is maintained. Better still, protect any connection point by installing them in a weather proof enclosure. Also ensure the antenna is intended for use outdoors but don’t over specify ratings or a higher price may be paid. No need for 1m underwater protection (IP67) if just rainfall will be experienced. Antennas don’t typically work underwater anyway.

The post It’s just a piece of cable, why should I care? appeared first on Siretta Limited.

What is a low profile antenna

A low profile antenna is designed for discrete installations so that it doesn’t look like a traditional whip or stubby style antenna and being fixed very closely to what it is mounted to. The low profile design is inconspicuous to avoid attention and offers an alternative for many IoT applications that require a wireless device to transmit a signal which is vertically polarised. As low profile antennas are relatively flat the radiating element is mounted in a horizontal plane and as a result the direct performance will be slightly affected. As such the low profile antennas are deisnged to use the mounting point as an extended ground plane to improve signal performance and remain hidden.

Mounting of the antenna

If the antenna can be mounted vertically, this helps improve the system performance but be mindful of the mounting surface. There are a number of groundplane dependent and groundplane independent products available from Siretta. Low profile antennas with a steel base are generally groundplane independent whilst others that have a PCB element encased in plastic housing are groundplane dependant. This will affect the radiating performance of the antenna and therefore care should be taken to use the corrcet type of antenna for the mounting surface as the radiation pattern when transmitting will be offset, affecting the transmission range.

Most low profile antennas for wireless IoT and telemetry applications have a screw threaded bolt through which the RF cable in retained. This means that no external cable is visible once the installation has taken place. Different mounting surfaces have different thicknesses and in the case of fibre glass or plastic mounting surfaces, consideration needs to be given to check whether the through hole section will be long enough to allow the mounting nut and washer to connect to the screw thread.

Cable length considerations

Low profile antennas tend to use a ¼ wavelength tuned dipole within a low height plastic enclosure. As with all antennas, the smaller the antenna used in the design, the more susceptible it will be to detuning and its performance be affected. This situation is made worse by the use of long cable runs. It is worthwhile keeping the cable run as short as possible to minimise RF loss over the length of cable. However if this cannot be avoided, it is worth considering a low loss RF cable and in the case of cellular communication, changing from a high frequency network band to a lower frequency network band will greatly improve signal performance.

Ensuring a waterproof fit

When using a low profile antenna it is possible to ensure a very tight fit to the mounting surface. In outdoor and mobile environments it is important to ensure that moisture does not get through the mounting hole and into the enclosure. Water ingress can be prevented or largely reduced by using an adhesive and/or rubber gasket between the antenna and the mounting surface. This is particularly important if the antenna is used in a mobile environment and is travelling at high speed.

The post Low Profile Antennas in IoT Applications appeared first on Siretta Limited.

When concentrating on the improvements in cellular signal transmission and reception in embedded design applications, similar transmission and reception rules are valid for the majority of today’s wireless systems. These include ISM bands such as 433, 868 and 2400MHz and other technologies such as WiFi, Sigfox and Zigbee / IEEE802.15.4 standards.

A cellular antenna can propagate on 700, 800, 850, 900, 1700, 1800, 1900, 2100 & 2600 frequencies. The propagation of these signal radiate in a straight line, operating in a line of sight basis. Although radio signals do bounce off and travel through certain materials, using the line of sight practice should be the first observation to make to improve signla integrity. There needs to be particular emphasis on the fact that the antenna receives or transmits the signal and not the wireless module.

Obstructions

Obstructions placed between the base station and antenna will absorb or bounce the signal to varying degrees. For instance a sheet of paper between a transmitting cell tower and a receiving antenna in a cellular environment would have virtually no effect, however if an antenna was inside a building or metallic enclosure, it would have a more dramatic effect. Likewise, geographic obstacles such as a hill or building between a cell tower and  receiving station could block a cellular radio signal entirely.

One simple way of overcoming obstructions in a line of sight communications environment is to elevate the radiating antenna. Many of Siretta’s Wall/Mount Outdoor antennas are supplied with different lengths of cable and using a loss loss cable solution it is possible to accommodate cable runs of up to 20 metres. This will give the installer a greater scope for installing the antenna as high above the ground as possible and preferably outside of a building focussing towards an area with the best cell site coverage. It is worth noting that less cable length equals less RF loss so this should be considered when specifying cable lengths for antennas.

When specifying an office or base station antenna, the engineer needs to ensure that the antenna, cable and connector configuration is of 50 Ohm impedance and the cable length is optimised for the site. Co-axial cable has differing levels of RF loss depending on the type of cable selected so it is advisable to have enough for the installation without too much surplus. Although installations vary from site to site, this can be overcome in the field by ensuring installers have carried out site surveys and have extension leads to allow for routing. These can be added or taken off at the discretion of the installing engineer. Similarly, care should be taken when fitting inter series RF adapters or link cables in line. Each adapter fitted inline to a cable increases the RF losses and reduces the overall system performance.

Losses

Regarding RF loss, the higher the operating frequency, the greater the loss per metre. In the United Kingdom, there are a number of bands available for use in cellular communication and as a result it can be possible to improve the enitre system performance by simply moving to a lower frequency. On the 2G / GSM network operating on the 900MHz band it is possible to transmit at 2 Watts whilst on the 1800MHz frequency it is possible to operate at 1 Watt. With a 2 Watt 900MHz system operating on twice the power, the working range will be significantly enhanced over an 1800MHz operating at 1 Watt.

Lower frequencies have longer wavelengths and as such distances between sequential crests of a sine wave are further apart, which mean that they are able to travel further. Therefore network operators who transmit on low frequcnies benefit the end user by being able to transmit over a greater distance and provide network coverage to more rural areas with less infrastructure. Higher frequency cellular bands are good in an urban environment with multiple cell sites as they are able to offer a higher transmission bandwidth to the connected devices within the same environment.

Network Operator

With most businesses designing and installing cellular equipment in to the field, the last factor to be considered is the cost of airtime and this is usually selected based on a commercial decision largely influenced by price. It is at this point where careful consideration should be given to the network operator and their service offering. Depending on the end application it may be necessary to consider looking at an alternative airtime provider which operates on a lower frequency band if reliable communication is required in remote rural areas.

Whilst each of these individual criteria is an important factor on its own, to ensure a reliable communication platform that operates effectively, you must consider all of these factors together and ensure that each element is chosen for the end application. This will ensure that you have a system which out performs expectations and operates reliably in the field with reduced downtime and costs whilst improving system performance.

The post Improving Cellular Signal Reception in IoT Applications appeared first on Siretta Limited.

There are 3 types of antenna design solution available to an engineer each with its own advantages and disadvantages. Design issues range from real estate available on a PCB to the amount of time required to get a product to market. Questions raised can be quite tricky to answer especially when a short time to market is required. Additionally, many antenna manufacturers are biased on their own particular area of expertise rather than providing the best solution from a full range of products.

Ceramic Antennas

Many ceramic antennas are available tuned to different technologies such as cellular, ISM, LTE and WiFi. They are amongst the most compact solutions available and require a dedicated space on a PCB with adequate ground plane clearance.

This will differ depending on the wireless technology used and the frequency of operation but as a guide, the higher the frequency, the smaller the wavelength and therefore the ground-plane. As the ground-plane needs to be taken into consideration for the antenna to function correctly you will need to take into account the recommended ground-plane size when considering the PCB real estate and not just the base antenna dimensions. Embedded designs using ceramic antennas will take the longest to design in to your solution as the PCB layout will require some tuning and this will take longer. In addition to the hardware design there will also be a requirement to perform emissions testing for the complete design to ensure RF interference is minimal and the system will not interfere with other systems.

Ceramic antennas tend to be the lowest cost solution overall. However, they are targeted at volume users and as such evaluation kits tend to be required for testing and evaluation with minimum order quantities required to achieve a lower price.

PCB antennas

PCB antennas answer the need for a pluggable solution which can be easily integrated in to the system utilising a micro RF connector. Many existing wireless modules incorporate a micro connector which can be connected directly to an embedded PCB antenna and provides a very simple method to incorporate an antenna into a system. These embedded PCB antennas are tuned to various frequencies and can be terminated with differing lengths of cable and connector styles which offer compatibility with most wireless modules available.

One consideration is the overall size of the enclosure to ensure the antenna fits. For instance, there are antennas built to a specific wavelength i.e. ¼ wave which are both tuned to work on a given frequency or frequencies and harmonics to cover a range of different network frequencies. As a result, each band of interest will have a different gain at a particular frequency and therefore one antenna may well fit a number of different applications.

Some applications are governed by the need to be the smallest possible size. For cellular solutions, we are generally spoilt in that there is a dense network coverage, especially in built up areas such as cities and industrial areas. Many engineers opt for having a true quarter wave antenna for their application, however, there are then issues with the size of the antenna. For example a 900MHz cellular network can provide up to 2 Watts and a ¼ wavelength at 900MHz is around 7cm, at 1800MHz a ¼ wavelength is around 3.5cm. As a result, the size of the antenna is directly affected by the frequency of operation and can be too large to fit in to the application, therefore, consideration must be taken to select the best overall solution.

Embedded PCB antennas are designed are easily attached to the inside of the enclosure via an adhesive pad allowing quick connectivity, offering reliable performance and flexibility of fitting away from other components prone to RF interference.

External Antennas

In some situations a metal enclosure has been specified which will block the RF signal as it creates a Faraday cage effect around an internal antenna. To overcome this, an internal cable assembly linking the wireless module to a bulkhead connector can bridge the gap allowing an external antenna to be fitted directly onto the bulkhead connector on the outside of the enclosure.

This option also gives the benefit of expanding the range of antennas available to be used on the application. This can be ideal for using with equipment which will be installed in areas of poor coverage or installed in difficult to access locations. It also allows an organisation to offer a range of ‘After Market Solutions’ which overcome specific installation challenges.

Each example of antenna solution brings its own advantages and disadvantages to the market and these need to be weighed up prior to selecting a solution. In practice, an external antenna generally performs better than an internal antenna. Therefore unless there is a strict requirement in the specification for an embedded antenna to be used – such as a vandal resistant or high IP rated environment then increasing the likelihood of good wireless communications has to be the highest priority using an external antenna solution.

Speak to Siretta for more information.

The post Successful Antenna Selection in Embedded IoT Applications appeared first on Siretta Limited.

As more electronics are integrated into ever decreasing sized enclosures and at a lower cost, it looks like corners are starting to be cut with respect to good engineering practice at the design stage. Below are some pointers with respect to designing in GNSS antennas into compact and handheld equipment.

Antenna Placement

The most important item to consider is the best siting for the antenna. Even with today’s latest generation chipsets, a GNSS antenna still needs a clear view of the sky especially during first acquisition when it needs to download the latest ephemeris data or on some occasions, a complete almanac.

This almanac and ephemeris data provides a virtual map to the GPS / GNSS receiver constellation allowing it to know the current and future locations and status of the satellites, relevant for that particular location. The almanac is a long-term picture of what the whole GNSS network is doing whilst the ephemeris is for a short-term picture. The delay when the GNSS receiver is first switched on is due to the latest ephemeris data being downloaded, which is essential for the GNSS receiver. The data is valid for around 4 hours and takes approximately 20 seconds to download with a clear line of site to a satellite. It takes longer if using multiple satellites, for instance if the GNSS receiver is moving during first acquisition.

The antenna needs to be facing the sky through a non-metallic enclosure. A metallic enclosure will prevent the RF signal being received by the antenna and cause a Faraday cage effect. Likewise, positioning the antenna near to obstructions such as power supplies, LCD displays or where large objects will be over the antenna should also be avoided as the shield will have a negative impact on performance.

Try to avoid routing cables across other electronic equipment or the back of screens, instead try to route around the perimeter of active electronic components. Whilst it is a good idea to keep the cable relatively short, (thin RF coaxial cable used on electronic equipment has quite a high loss at 1575.42 MHz) and is susceptible to interference. However, the length consideration is not as essential as placement as most GNSS antennas have a 1 or 2 stage pre amplifier depending on GNSS receiver used.

Smaller is not always Better

When designing in a GNSS antenna, do not always look for the smallest possible antenna. Although this can seem attractive, particularly in hand held or portable equipment when size is everything, the effect of a smaller GPS antenna means it is more sensitive to de-tuning. GNSS works on a spot frequency of 1575.42MHz rather than a frequency range. This means that when other materials cover it – human tissue, LCD screens, metal, it de-tunes the antenna away from this frequency. The smaller the antenna, the more susceptible it is to the de-tuning effect, which results in a reduced GNSS signal being received.

As a general rule a 25mm x 25mm patch antennas might be considered too large but will work well, whilst a 10 x 10mm patch antennas will tick the size requirement but could take a longer time to get the first fix and sub-sequentially a navigation state. Similarly, helical antennas sound good on paper but during field trials are poor when compared to a patch antenna with a comparable pre- amplifier. The sweet spots seems to be around 17 x 17mm where the thickness of the antenna with LNA underneath using a 2mm thick ceramic patch gives an overall thickness of around 6mm. This sized patch antenna provides good resistance to noise and reasonable performance to acquisition whilst keeping a small footprint.

Low Noise Amplifier

Siretta provide GNSS antennas which provide either a 1 or 2 stage low noise amplifier (LNA) to optimise the final design. 1 stage designs provide a gain of around 12-18dB and are reliant on either the GNSS receiver having its own LNA or a very short cable run. 2 stage LNA solutions provide a gain of between 25-30dB and are more popular on antennas where the GNSS receiver does not have an amplifier. Although the preconception of the higher the gain the better the performance, this is not always true. If the gain is too high constantly, this can have an over saturation effect on the GNSS receiver, de-sensitising the RF front end over time and causing poor navigation.

In addition, using a high gain 2 stage LNA also amplifies the noise received at the patch antenna and results in errors being picked up at the receiver which must be removed from the position calculation.

Contact Siretta for further information.

The post GNSS Antenna Selection for Embedded Applications appeared first on Siretta Limited.

Locations with telemetry equipment include vending machines, bus stops fitted with RTPI (real time passenger information) equipment, utility boxes acting as a local information gateway from homes back to service providers and remote weather stations for transmitting local weather to a centralised point. All have a critical requirement for ensuring products are built to last in their particular environment and wireless connectivity over a cellular network is becoming a low cost way of interacting with remote sites.

Use a Low Profile Antenna

Although most cellular antennas are vertically polarised, a growing trend of low profile antennas are being introduced in to the market. These are designed to be fitted using the through hole bolt which passes through a hole on the enclosure. This ensures that the antenna cannot be removed without access to the inside of the enclosure and no cabling is visible. Good quality low profile antenna products from Siretta are designed with robust plastic enclosures to give adequate protection against all but the most sustained attack. These offer cellular connectivity and often provide multi technology operation including ISM, WiFi and GNSS all in one physical antenna casing.

Elevate the Antenna

Cellular communication operates on a line of site principle so it is advantageous to raise the height of the antenna above ground level as high as possible. This gives the additional bonus of keeping the antenna out of reach whilst providing improved communications at the same time.

Cables in these installations can be easily targeted as they can be seen routed up sign posts, bus stop poles, drainpipes and other suitable mounting points; therefore, it is recommended to route these cables through a protective conduit or within a post. Alternativel,y route the cable underground to minimise vulnerability and reduce elements of the system being targeted. Siretta offer outdoor wall/pole mount antennas which are water resistant and come with a mounting bracket for fixing to poles or the side of buildings. In addition they are provided with long low loss cables which offer a good link budget and can place the antenna in an elevated position which improves the performance of the installation.

For very weak signal areas such as remote rural sites with only one cell site available, a Yagi antenna from Siretta can be installed at a high point and pointed in the direction of the cell site to offer a good signal connection to the remote equipment. To facilitate installation of the antenna, Siretta also provide the SNYPER cellular signal analyser which can provide a real time graphical output to help determine the optimum placement of the antenna.

As with all exterior mounted antennas, it is a good idea to add a lightening surge arrestor to the feed line to reduce the risk of high voltage transients destroying communications equipment downstream. This simple GDT (Gas Discharge Tube) device is a simple low cost ‘insurance’ premium which could avoid costly equipment replacement and engineer call outs. The Siretta accessory line contains surge arrestors with the most common connection types in the market today.

Hide the Antenna

Providing the equipment is not inside a metal enclosure (RF signals do not transmit well inside a metal case), internal antennas can be used. These are available with varying lengths of cable according to the distance between antenna mounting site and telemetry unit. If the antenna is going inside equipment then a less rugged non weatherproof antenna can be used to directly connect to the communication equipment. Siretta provide a comprehensive range of embedded antennas or adhesive antennas to install within your enclosure.

The above pointers should always be observed in all installations to overcome concerns about longevity, performance and robustness of products installed in the field. Field trials are essential to ensure that the end solution is robust. Once field trials are completed satisfactorily then you can be sure that you have a practical compromise to maintaining suitable signal integrity whilst not having any weak spots in your system design.

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